1. Field of the Invention
The present invention relates to rotary solenoids.
2. Description of the Prior Art
Rotary solenoids are well known in the art. These conventional prior art rotary solenoids employ return springs on the return stroke of the solenoid to return the rotor to the initial rest position upon deenergization of the solenoid coil. However, the use of such a return spring reduces the forward torque present on the forward stroke of such rotary solenoids while, in addition, restricting reduction in size of such rotary solenoids because of the space necessary to accommodate the requisite return spring. Prior art attempts to improve the forward torque curve of the solenoid in the energized state have involved the use of a variable cam formed air gap in addition to the conventional return spring. However, the aformentioned disadvantages associated with the requisite return spring have not been overcome by such prior art arrangements. In addition, the magnetically permeable material forming the housing and rotor of prior art rotary solenoids undergoes normal aging over a period of time which aging produces undesirable effects, such as resultant sticking of the rotor due to residual magnetism present in the housing and rotor. In addition, prior art rotary solenoids, to applicant's knowledge, have not satisfactorily achieved optimum efficiency due to this failure to efficiently balance the factors of coil size and iron volume. Accordingly, the saturation flux density of the iron used in constructing the housing and rotor of such prior art devices is effectively limited by the associated saturation flux density of the material used. Thus, for a given housing size for such prior art rotary solenoids, there is a given maximum limit for the saturation flux density dependent on the material selected with the size of the housing effectively limiting the size of the coil. Moreover, as stated above, the coil size is effectively limited even further due to the necessity of providing space in the housing for the return spring. These disadvantages of the prior art are overcome by the present invention.